The present invention relates to a covering for an architectural opening, and in particular a covering which requires extra weight to be incorporated into at least one of the rails of the covering.
It is known to add extra weight to a rail of a covering. This may for instance be done to provide extra stability for the rail, so as to prevent it from wobbling during raising and lowering.
Applying extra weight to a rail of a covering can also be advantageous in the case of, for example, pleated and/or honeycomb blinds to facilitate lowering of the blind. The extra weight helps to overcome the friction of the cords that run through the pleated and/or honeycomb material. At every hole in the fabric through which these cords pass, some friction is exerted on the cords by the edges of the holes. This friction increases as the material is extended. In a collapsed condition, the pleat/honeycomb material extends substantially perpendicular to the cords. Therefore, in this condition, the cords may not even contact the edges of the holes and the friction will be low. However, as the fabric extends, the angle between the pleat material and the horizontal may go from 0° to for instance 45° or 60° or more and in such cases, the edges of the holes will contact the cords and exert a frictional force thereon. The total friction will of course also increase with the height of the blind, as there will be more holes for the cords to pass through. Inserting extra weight into the lower rail of the blind will help to overcome this friction.
Typically, most rails have in essence two longitudinally extending side walls connected together by a central wall. The side walls and the central wall are usually an integral unit formed by extrusion. The edge of the fabric is disposed on one side of the central wall, and the cords (for lifting, guiding and/or supporting the covering material) may extend through the central wall to a cord chamber on the other side. After assembly, the cord chamber, which is bounded by the central wall and the side walls of the rail, may be closed with a cover which can be slid into grooves provided at the end of the side wall.
In known coverings, the weight is normally shaped as a metal bar. This bar is attached to the inner surface of the central wall, i.e. the surface that forms part of the boundary of the cord chamber. Known means of attaching the bar to the central wall include glue and other adhesives, double-sided tape, Velcro, for example.
This conventional way of applying extra weight, however, has several disadvantages. For example, during transport the weight may become dislodged and may start to slide in the rail. This may cause damage to end caps of the rail that will usually be mounted on either end of the rail. Furthermore, in conventional rails, the location of the weights may not be optimum. This is because the weights have to be positioned such that they do not interfere with the cords which enter the rail via holes in the central wall of the rail. Thus care has to be taken when mounting the weights so as to ensure that the weights do not obstruct the holes and/or the routing of the cords. Accordingly, the positioning freedom of the weights is limited. In some instances, the weights may even have to be cut to fit between adjacent holes. A further consequence is that the weights must be mounted at an early stage of assembly, in any case prior to assembling the cords, because if the weights are mounted afterwards, the cords may become trapped between the weight and the central wall of the rail. However, mounting the weights at such an early stage may be disadvantageous. For instance, an installer may only find out during installation of the blinds that the number of weights is insufficient, or the position of the weights is wrong. In conventional rails, it is difficult to add extra weights at a later stage and it is also difficult to adjust the position of the weights later if required.